In human anatomy, the subtalar joint, also known as the talocalcaneal joint, provides for the articulation between the talus (ankle bone) and the calcaneus (heel bone). A malalignment of the subtalar joint with the bones being provided with this articulation, is a major causative factor or exacerbating factor in many foot pathologies.
Flexible flatfoot is a common such foot disorder caused by hyperpronation and a resulting flattening of the longitudinal arch of the foot in conjunction with excessive calcaneal eversion and forefoot abduction. When the foot is excessively pronated, the talar head rotates medially on the calcaneus and the lateral process of the talus rotates forward.
In general terms, such an excessive pronation may be congenital, or it may occur later in life due to posterior tibial tendon pathologies. Posterior tibial tendon pathologies may be caused by trauma, overuse, inflammatory disorders, and other reasons or combinations of such, or a progressive deformity originating with a congenitally pronated foot.
In addition to causing flat feet, excessively pronated feet contribute to a wide variety of foot ailments including but not limited to: tendinitis, plantar fasciitis, bunions, hammertoes, hallux limitus, and generalized foot pain. Symptoms frequently include pain, weakness, fatigue, and throbbing or cramping discomfort. In children, the resulting symptoms may also include refusal to participate in athletics or refusing or refraining from walking long distances.
Conventional non-invasive treatments, which attempt to provide a means for maintaining proper bone and foot alignment, include foot orthotics, ankle braces, and shoe modifications adapted to properly position and support the foot when bearing weight. Such devices and modifications can be very expensive, especially in younger patients who frequently outgrow them and require replacements.
Arthroereisis is conventionally defined as an operative procedure limiting motion in an abnormally or over-mobile joint. In a flat-footed, hyperpronated patient, a subtalar arthroereisis is employed to engage and restrict the motion between the talus and calcaneus bones. Conventionally, this restriction of motion therebetween is accomplished by placing a mechanically engaged surgical implant within the sinus tarsi, a space, between the talus and calcaneus.
A number of devices are conventionally available for sinus tarsi implantation. These conventional implants are designed and structurally configured to mechanically engage with adjacent bone surfaces and once mounted they restrict subtalar joint motion. The implants purport to improve the alignment of the foot of the patient, and thereby provide an assist in the reduction of foot and ankle pain and pathology.
However, most such devices are of a one-design-fits-all configuration and leave a vast majority of the size, shape, and engagement position to what can best be described as the surgeon or medical professional's experienced estimate. With size, engagement method, positioning, angling, and a host of other factors to consider, there is considerable room for error.
Further, because these threaded or screwed or similar elongated implants employ a permanent mechanical engagement with the bones involved, at a very small space on the circumference of the implant, there is an immense amount of force imparted to each respectively engaged bone on the very small surface area of engagement with the implant.
This small area of engagement, and due to a mismatch in the chosen implant shape, and the sinus tarsi anatomy, there are abnormal impact stresses applied to the bones. Such stress is a common cause in treated patients of post-arthroereisis pain which is generally one of the major factors patient's choose such implants in the first place. While this mechanical engagement and one-design-fits-all concept works well in mechanical components, in the human body, employing a hard metallic member of a singular shape or configuration, and implanting it through mechanical engagement in a biologically diverse population of patients all having infinitely variable bone and joint positioning aspects, is less than ideal.
For example, U.S. Pat. No. 7,033,398, (Graham) teaches the employment of a generally cylindrical implant having two sections including a frustum of a right cone portion as well as an integral extension. The frustum or coned portion is operably positioned within the lateral or sinus region of the sinus tarsi and a smaller diameter cylindrical portion of the implant is engaged on the medial side of the implant and is operably engaged within the canalis tarsi.
The surface of the disclosed implant contains channels or threads or a roughened texture in selected engagement regions. These engagement regions mechanically engage with the contacting bones in small surface areas to achieve a mechanical engagement with the bones being stabilized.
As taught, the Graham reference, included herein by this reference, is an exemplar of the current state of the art in this type of implant where cylindrical elongated implants, are mechanically engaged with adjacent bones, at very small surface area contact points, to maintain a certain positioning. As noted, choosing the right size, and shaped implant, and contact engagement surfaces, and angle of engagement, amongst other variable factors, is up to the medical professional as is positioning. Further, when deciding at what position to position the foot bones of the patient, to employ the implant to hold that position, it is again a professional educated guess, since the implant does not determine the ultimate position of the engaged bones. Instead, the foot is held where the medical professional believes is the proper weight-bearing position, and then the insert is engaged mechanically. This engagement holds the contacted bones in a position relative to each other to provide a means to maintain the limited motion for the patient to be able to acquire that proper position when healed. Consequently, the medical professional must use x rays and professional estimates of what is needed and how it should be engaged which can be less than accurate and fail to product optimum patient outcomes.
As such, there exists an unmet need for an implant adapted for positioning in the sinus tarsi, which is custom-configurable to correct an excessive talar displacement and calcaneal eversion in each respective individual patient. Such a device should be inert when positioned in the body. Further, such a device should be modeled, and thereafter formed, from the actual images of bone configurations of each respective patient, while their foot is weight-bearing at the proper angle, to thereby yield an implant having an exterior surface configuration which is adapted to match the weight-bearing bones and contact surfaces each patient individually, at the largest possible contact surface areas. Such an implant should thereby yield maximum comfort concurrently with maximized results and improvement to the bio mechanics of the foot during weight bearing since once inserted, the surfaces of the implant will cause the contacted bone surfaces, to maintain the weight-bearing position ascertained in the 3D imaging as proper.
In this respect, before explaining at least one embodiment of the implant invention and method herein in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangement of the components set forth in the following description or illustrated in the drawings nor the steps outlined in the specification. The disclosed sinus tarsi area implant is capable of other embodiments and of being practiced and carried out in various ways as those skilled in the art will readily ascertain once educated in the novel device and method of this application.
Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting in any manner. As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for designing other methods and systems for carrying out the several purposes of the sinus tarsi implantation device disclosed herein. It is important, therefore, that the claims be regarded as including such equivalent construction insofar as they do not depart from the spirit and scope of the present invention.